LDL-C · "bad" cholesterol
LDL cholesterol: what your result means
LDL is the cholesterol that ends up in artery walls. It is the number most cardiovascular treatment aims at — and the one where "normal for the lab" and "good for you" differ most.
What it measures
Low-density lipoprotein carries cholesterol from the liver out to the rest of the body, and LDL cholesterol measures how much is being carried that way. On most reports it is calculated from total cholesterol, HDL and triglycerides rather than measured directly, which is why very high triglycerides make it unreliable.
Why it gets tested
To estimate cardiovascular risk and to decide on and monitor treatment. It is checked in routine health assessments from midlife, earlier where there is a family history of early heart disease or of familial hypercholesterolaemia, and regularly once somebody is on a statin.
Typical ranges
Laboratories commonly print an upper limit around 3.0 mmol/L (about 115 mg/dL), but the meaningful target depends on your overall risk rather than on that range. Someone who has already had a heart attack is usually treated to below 1.4 mmol/L (about 55 mg/dL), while a genuinely low-risk person may need no target at all. One printed range cannot express that, which is why the flag on the report misleads in both directions.
Compare against the range printed on your own report, not this one. Laboratories differ, and yours is the one your doctor is reading.
What a high result can mean
Diet, weight, activity and genetics together. A markedly high LDL from a young age — particularly alongside heart attacks in the family before 55 in men or 65 in women — raises the possibility of familial hypercholesterolaemia, which affects roughly 1 in 250 people and is badly under-diagnosed. An underactive thyroid, kidney disease, pregnancy, cholestasis and some drugs also raise it.
What a low result can mean
Usually treatment doing its job, and there is no evidence that a low LDL on a statin is harmful. Very low untreated LDL can accompany an overactive thyroid, malabsorption, liver disease, chronic infection or malnutrition, and occasionally has a genetic cause — there, what surrounds the number matters more than the number.
What moves it
Saturated fat particularly, body weight, thyroid function, pregnancy, alcohol, and a substantial inherited component. Acute illness and the weeks after a heart attack lower it temporarily, so a sample taken then understates the usual level.
What usually happens next
A high result is usually repeated, read with the rest of the lipid panel, and set against overall cardiovascular risk — blood pressure, smoking, diabetes, family history, sometimes ApoB or Lp(a). Depending on that total, what follows is lifestyle change, a statin, or both, with a recheck after about three months.
Common questions
Is LDL the same as total cholesterol?
No. Total cholesterol adds LDL, HDL and a share of the triglyceride-carrying particles together. Two people with the same total can carry very different risk, which is why LDL — or better, ApoB — is what treatment is aimed at.
Do I need to fast for a cholesterol test?
Usually not any more. Non-fasting samples are accepted for most purposes. Fasting is still sometimes requested when triglycerides are very high, because LDL is calculated from them and the calculation breaks down.